According to the heretofore-known state of the art, applicator wipers, as well as slot wipers and thin-layering, or impregnating air wipers are rigidly mounted (fixed). It also has been known to profile the edges of the wiper strip (also called a wiper blade). The shapes of these profiles vary generally the wiper profiles are narrow, because otherwise the application pressure would be too high. The term of "too high" is to be understood as follows:
The term "too high", with respect to a substance to be applied which lies freely on the substrate in front of the wiper strip, means a pressure under which the material would escape in a direction opposite to the direction of movement and this way would evade the intended application, particularly a coating application- in an undesirable manner, so that large application quantities could not be handled. The wider the application surface covered by the wiper, the higher is the total pressure, which increases proportionally with the surface according to the basic principle of hydraulics, or the counterpressure resulting therefrom at the wipers.
This is the reason why, according to the present state of the art, coating and impregnating installations with wipers have to be strong and dimensioned correspondingly with considerable material consumption and expenses even for a relatively reduced width of the applicator profiles.
The efforts to keep the wiper profiles according to the present state of the art as narrow as possible in their effective areas, almost blade-like, are therefore based on technological reasons and technical (physical) limits and is to be considered a specific feature of the heretofore-known state of the art.
As far as heretofore known, the coating or impregnating wiper spars (also named doctor blades) are as a rule fastened at both their ends, or mounted rigidly, or adjustably with respect to the position of the sheet material to be coated, whereby in the construction special attention is given to the stability against deviations or to possibilities for the correction of unavoidable deviations.
In order to illustrate the precision in manufacturing and setting of such devices, the following example may be mentioned: If a liquid substance with the fluency of water has to be applied in an amount of 50 g/m.sup.2, this will correspond to a layer thickness of 5/100, i.e. five hundredths of a millimeter. If this coating has to be applied with a precision of plus or minus 10%, this corresponds in the substance quantity to plus/minus 5 grams and in the layer thickness to plus/minus 5/1000 mm. Since in practice, the width to be coated usually averages 2 to 3 m and more, the requirements for stability, for the operational and adjustment precision of such installations are usually very high. Each particular application process generates an application pressure depending on several parameters or makes it a requirement. Since its magnitude can not be calculated in advance, almost any application process makes it necessary to perform readjustments at the wiper device. It is therefore appropriate to keep the edges, or surfaces of the wiper profiles effectuating the application process and therefore exposed to the application pressure, as narrow as possible (the term doctor blades used in practice makes this very clear).
Some sheet materials are so sensitive that they can not be touched during the coating or impregnating; e.g., fleece, when not reinforced, falls into this category. For applications on this type of material wiper devices are not suitable. In order to reinforce the fleece through impregnation, presently very cumbersome and expensive technologies have to be used.